The exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase materials (liquids and solids) that constitute particulate matter (“PM”). Catalyst compositions, typically disposed on catalyst supports or substrates, are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing CO and HC emissions is an oxidation catalyst (“OC”) device. The OC device includes a flow-through substrate with a catalyst compound applied to the substrate. The catalyst compound of the OC device induces an oxidation reaction of the exhaust gases once the OC device has attained a threshold or light-off temperature. One type of exhaust treatment technology for reducing NOx emissions is a selective catalyst reduction (“SCR”) device. The SCR device includes a substrate, where a SCR catalyst compound is applied to the substrate. A reductant is typically sprayed into hot exhaust gases upstream of the SCR device. However, the SCR device also needs to reach a threshold or light-off temperature to effectively reduce NOx. Following a cold start of the engine, the OC device and the SCR device have not attained the respective light-off temperatures, and therefore generally may not effectively remove CO, HC, and NOx from the exhaust gases.
One approach for increasing the effectiveness of the OC and the SCR devices involves providing an electrically heated oxidation catalyst (“EHC”) device upstream of the OC device and the SCR device. The EHC device may include a monolith and an electrical heater. The catalyst of the EHC device is heated to a respective light-off temperature, which is the temperature at which rapid HC oxidation occurs within the oxidation catalyst compound disposed on the EHC device.
A generator may be provided to convert mechanical energy from the engine into electrical power needed for various electrical loads. In one approach, the generator may be disconnected from a vehicle battery while providing electrical power to the electrical heater of the EHC device to heat the catalyst of the EHC device. However, disconnecting the generator from the vehicle battery for an extended period of time reduces battery life. Accordingly, it is desirable to provide an approach for effectively providing electrical power to the electrical heater of the EHC device while reducing the impact on battery life.